Color temperature control



June 6, 1967 L. Dil-:TCH ETAI.

CoLoR TEMPERATURE CONTROL original Filed Feb. 5, 1964 Fwd mJOmhZOU United Statesl Patent O 3,324,236 CULUR TEMPERATURE CONTROL Leonard Dietcli, Skokie, and James G. S. Chua, Roselle, Ill., assignors to Admiral Corporation, Chicago, lll., a corporation of Delaware Continuation of application Ser. No. 342,726, Feb. 5,

1964. This application Nov. 4, 1966, Ser. No. 604,094

S Claims. (Cl. 17d-5.4)

This application is a continuation of our co-pending application Ser. No. 342,726, filed Feb. 5, 1964, and now abandoned.

This invention relates to color television receivers and specifically to means in the receiver for optimizing both monochrome and color presentations. More specifically,

the invention is concerned with the color temperature (or tint of the raster) of the color television receiver screen.

Three gun shadow mask type picture tubes are normally used in color television receivers today. As is Wellknown, such tubes have mosaic targets or screens consisting of a plurality of groups of three dots of the primary color phosphors red, blue and green. These groups or clusters are called triads. Accurately displaced from the target is a shadow mask comprising a metal screen having apertures positioned adjacent to and in registration with corresponding triads. The three electron Idifferent temperatures as explained on page 4-32 of Television Engineering Handbook by Fink, McGraw-Hill Book Company, 1957. There are numerous controls and adjustments on the color receiver for setting up the white condition, since there are many variables such as manufacturing tolerances in the electron guns which, in efect, changes their translation characteristics, efficiency of the color phosphors7 the proportion of electrons blocked by the shadow mask, etc., involved. A c-ommon set of controls in use today are screen controls, which determine the cutotf characteristics of the electron guns, and drive controls which aifect the translation efficiency of the guns.

It is well-known that the avera-ge television viewer prefers a monochrome picture which is produced by phosphors having a slightly bluish content. This is due to the 'fact that a little blue tends to make for apparently winter-whites. Picture tube manufacturers have long recognized this fact and have constructed monochrome picture tubes accordingly. On the other hand, it is wellknown that the best color pictures are produced on a background which is somewhat yellow or sepia in tone (a low intensity` desaturated yellow appears sepia in color). With a bluish screen satisfactory color production is difficult to achieve. Flesh tones especially (the standard by which the viewer adjusts his color set) are extremely difficult to obtain with a bluish raster. With a sepia screen, however, the overall effect is one of warmth and ilesh tones are readily obtainable. It should be noted that -calling the raster color yellow and sepia is not inconsistent since the highlight areas are yellow and the lowlight areas are sepia.

At the present time, color sets are probably used for monochrome reception more often than for color reception. While this situation is bound to change as color programming displaces monochrome programming to a greater extent, color receivers will still be utilized for both Patented June 6, 1967 ICC color and monochrome viewing. Thus both screen conditions are, and will continue to be, desirable depending upon the program material received.

The present invention is designed to meet 'both of these conditions and, in effect, allow the viewer an -option in the type of background produced on his set. Thus, in accordance with the illustrated embodiment of the invention, a color temperature control is provided for shifting the color temperature of the light output from the receiver along an axis linking blue and yellow. Thus for monochrome the screen may be set toward blue and for color reception the screen may be set toward yellow.

Accordingly, the principal object of this invention is to provide a novel color television receiver.

Another object of this invention is to provide a cornpatible monochrome-color receiver having provision for adjusting the raster color of the screen.

An additional object of this invention is to provide means in a color television receiver for shifting the raster color of the screen 'between blue and yellow.

Further objects of this invention will be apparent upon reading of the detailed specification in -conjunction with the drawing in which a partial block, partial schematic dia-gram of a television receiver incorporating the invention is shown.

In accordance with the preferred embodiment of the invention, a variable direct current voltage is coupled to the electrode means in the picture tube electron gun beam generation system for varying the relative bombardment levels of at least tw-o of the different colored-light emitting phosphors and thus effecting a change in the raster color of the screen.

Referring now to the drawings, an antenna 1t) is coupled to a block 11 which is indicated as including an RF amplifier, an IF amplifier and video and audio detectors. The circuitry included in block 11 is considered conventional in the television art and needs no further description. A block 12, labeled AUDIO, is coupled to block 11 and includes circuitry for reproducing the audio accompaniment of the television signal received by antenna 10. Block 13, labeled VIDEO AMP, likewise contains circuitry for reproducing the monochrome information, i.e., the brightness or luminance signal Y, of the picture portion of the televised signal. Block 14, labeled SCANSION VOLTAGES and HIGH VOLTAGE, includes circuitry for developing the horizontal and vertical sweep voltages necessary to scan the electron beams across the face 0f picture tube 15 and the high voltage operating potential required by picture tube 15. The scansion voltages are coupled to a set of deflection windings 17 which generate the electromagnetic forces for scanning the electron beams. rlhe high voltage from block 14 is coupled, over a lead 16, to appropriate electrodes (not shown) in picture tube 15.

The description heretofore (as well as the drawing) has 'been brief since it is believed that those skilled in the art have more than adequate knowledge of this conventional phase of the television art to enable them to understand the circuit without elaboration.

Block 20 includes the color circuitry for the television receiver and is labeled, BURST AMPLIFIER, BAND PASS, SUBCARRIER OSC. and DEMODULATOR. This terminology -will be understood to describe circuitry for accepting a modulated color information signal, accepting and amplifying the color burst signal, regenerating, via a subcarrier oscillator and the color burst signal, the color reference signal and demodulating the color information signal. The output of block 20 is coupled to a matrix network in block 21 where circuitry is incorporated for obtaining a set of three color diiterence signals, namely, an R-Y, a G-Y and a B-Y signal.

Three color difference amplifiers comprising triode type vacuum tubes 30, 40 and 50 are shown. Tube 30 has an anode 31, a cathode 32 and a control grid 33. Similarly, tube 40 has an anode 41, a cathode 42 and a control grid 43 and tube 50, an anode 51, a cathode 52 and a control grid 53. The control grids are individually connected ,to matrix 21 and the cathodes are grounded. Load resistors 34, 44 and 54 are connected from a source of positive potential |V to anodes 31, 41, and 51, respectively. For illustrative purposes only, tube 30 is labeled R-Y, tube 40, G-Y and tube 50, B-Y. These tubes are conventionally referred to as color difference amplifiers and merely translate the color difference signals produced in matrix 21.

Picture tube 15 is shown to be of the three gun type. The red gun comprises cathode 38, control grid 37 and screen grid 39 (there are additional operating electrodes which have been omitted for simplicity). Similarly the green gun comprises cathode 48, control grid 47 and screen grid 49 and the blue gun, cathode 58, control grid 57 and screen grid 59. Screen grids 39, 49, and 59 are fed from a block 65 labeled, SCREEN CONTROLS, which will be understood to include means for adjusting the D.C. potentials of these grids and hence affect .the cutoff points of the guns. In the illustrated embodiment, the individual cathodes are driven by the luminance signal from video amplifier 13. In the case of the red gun cathode 38, the luminance signal is directly impressed. In the cases of the green and blue gun cathodes 48 and 58, respectively, the luminance signal is impressed through potentiometers 66 and 67 respectively. The latter potentiometers are commonly called drive controls. By proper adjustment of the screen controls (not shown) in block 65 and potentiometers 66 and 67, the color tempearture of the light output from the target of picture tube 15, (the tint of the raster) under monochrome reception conditions, may be set to be slightly bluish and will not change appreciably for different overall brightness levels. This is a set up adjustment, which is generally performed by a qualified service technician, as distinguished from a viewer or customer adjustment. As mentioned previously, `these adjustments are necessary since manufacturing tolerances and color phosphor efiiciencies vary to a large extent and in fact the three electron guns, in cooperation with the picture tube, constitute .three separate .translation systems whose gain and cutoff characteristics must be matched to each other.

Control grid 37 is coupled to load resistor 34 through the parallel combination of capacitor 35 and resistor 36. Thus the amplified R-Y color difference signal is coupled to the control grid of the red gun of picture tube 15. Similarly, green gun control grid 47 is coupled, through the parallel combination of capacitor 45 and resistor 46, to load resistor 44 and blue gun control grid 57 is coupled to load resistor 54 through the parallel combination of capacitor 55 and resistor 56. Thus, the appropriate amplified color difference signals are impressed upon the corresponding control grids of the tri-gun picture tube for determining the electron stream density from each gun. The color difference signals, in cooperation with the luminance signal, determine the color (both hue and saturation) and brightness level of the reproduced picture.

In the set up procedure previously mentioned, the effect of the control grids was not discussed, although it should be apparent that for black and white reception, the color difference amplifiers operate in a quiescent condition and a predetermined potential is impressed upon these control grids. In other words, the set up control settings are not independent of the color difference amplifiers although the set up procedure itself is.

The foregoing description has ignored the effect of elements 60-63. This group of elements comprises a potentiometer having a resistance element 60 coupled between +V and ground with a movable tap 61 adapted for sliding contact with resistance element 60. Movable tap 61 is coupled to the junction of resistors 62 and 63 which are serially connected between green control electrode 37 and blue control electrode 57. It will be seen that the position of movable tap 61 will affect the potentials applied to control grids 47 and 57 and consequently the raster color of .the screen may be changed by moving tap 61. This is so since the white light normally produced represents a mixture of red, green and blue in certain proportions and under the new conditions, the proportions have been changed.

In practice, resistor 62 is approximately three `times the value of resistor 63 which results in a 3 to 1 effect ratio, that is, the blue gun is affected more than the green gun by movements of tap 61. The values of resistance element and resistors 62 and 63 are selected with a view to the other components in the circuit, such that over the range of movement of tap 61 the raster color of the light output from the screen may be changed between slightly blue and yellow. Preferentially, movable tap 61 is accessible to the viewer and becomes a customer operated control along with the normal customer controls such as brightness, contrast, color intensity, hue, channel selection, fine tuning and volume.

Thus during reception of a monochrome program the viewer may adjust movable tap 61 to make the picture screen appear slightly blue which, as previously explained, makes for much better monochrome picture reproduction. On the contrary, during reception of a color program the movable tap may be adjusted to make the screen yellow in color which greatly enhances the color reproduction and gives an overall warmth to the reproduced display. Of course, intermediate settings may be utilized in accordance with individual preferences.

A further advantage of the invention resides in the fact `that the normal raster color of a television receiver, properly set up, has a tendency to change with aging of the components in the receiver. Consequently the receiver may exhibit objectionable raster color shifts over a period of time, which would normally require service adjustment. With the use of a color temperature control which is customer accessible, minor variations in raster color may be compensated for, and in fact are not even noticeable except at the extreme ranges of the control.

It should appear obvious that the color temperature control may be designed to operate with other combinations of guns and need not be limited to the blue and green guns as described. However, these two guns most readily produce the desired color temperature control variation from blue to yellow, which are the colors desired for optimum monochrome and color viewing. It will also be seen that the cost of adding this control is nominal and the results obtained thereby are quite striking.

Purely by way of illustration and not of limitation, the following representative values for the circuit of the drawing are given:

36, 47, 56 ohms 100,000 60 35, 45, 55 microfarads-- .01 60 ohms 500,000 62 megohms 3.3 63 do 1.5 30, 40, 50 Tube type 6GU7 15 Picture tube 21FJP22 monochrome and color viewing. It is understood that numerous modiications land changes in the prefer-red embodiment of the invention may be made by those skilled in the art without departing from the true spirit and scope thereof.

We claim as our invention:

1. In a color television receiver including a picture tube having an electron gun beam generation system displaced from a target consisting of a plurality of groups of different colore-d-light emitting phosphors, and means providing scansion of said target by an electron beam to produce a raster;

each phosphor in each of said groups emitting its` associated colored-light upon bombardment by electrons from said electron gun system;

said electron `gun system including electrode means capable of controlling the electron beam density thereof and determining the bombardment level for said different phosphors to establish a given color to said raster; and

means coupling .a voltage to said electrode means for simultaneously changing the relative bombardment levels of at least two of said dilerent colored-light emitting phosphors, regulation means determining the ratio of the simultaneous change in the Vrelative bombardment levels as between said two different colored phosphors, and said regulation means causing the color of said raster t-o vary substantially along lancks temperature locus.

2. 'In a color television receiver including a picture tube having an electron gun beam generation system displaced from a mosaic target consisting of a plurality of groups of different colored-light emitting phosphors, and means providing scansion of said :target by an electron beam to produce a raster;

each phosphor in each of said groups emitting its associated colored-light upon bombardment 'by electrons from said electron gun system;

said electron gun system including electrode means capable of controlling the electron beam density thereof `and determining the bombardment level for said different phosphors to establish a color for said raster;

and means coupling a variable direct current vol-tage -to said electrode means for differentially changing the relative bombardment levels of -at least two of lsaid different colored-light emitting phosphors in accordance with a predetermined ratio to cause the color of said raster to vary substantially along Plancks temperature locus.

3. In a color television receiver including a picture tube having three electron guns displaced from 4a mosaic target consisting of a plurality `of groups of three different colored-light emitting phosphors, each phosphor in each of said groups emitting its associated colored light upon bombardment by an electron stream from :a corresponding one of said electron guns;

each said electron gun having an electrode system capable of controlling the density of said electron stream generated thereby;

means coupled to said electrode systems controlling the bombardment level for their associated different colored-light emitting phosphors and establishing a given color temperature for the light emitted from said mosaic target;

a col-or difference signal translation means coupled to the electrode systems of each of said electron guns; and means including a voltage divider coupled to at least two of said color difference signal translation means for diierentially varying the relative density of the electron streams generated by the electron guns controlled by said two color diterence translation means, said voltage divider being adjustable for translating the composite color of said three-colored phosphors substantially along IPlancks temperature 5 locus.

4. In a color television receiver including a picture tube having three electron guns displaced from a mosaic target consisting of a plurality of groups Iof red, green and blue light emitting phosphors, each phosphor in each of said groups emitting its associated colored light upon bombardment by an electron stream from a corresponding one of said three electron guns, each said electron gun having an electrode system capable of controlling the density of said electron stream generated thereby;

bias means coupled to said electrode systems controlling the bombardment level for said different colored-light emitting phosphors and establishing a given color for the light emitted from said mosaic target;

three color difference signal translation means having outputs coupled to the electrode systems of said electron guns respectively;

circuit means coupling red, green and blue color difference signals to the inputs of said color difference signal translation means, respectively;

a voltage divider coupled to the output of the color difference signal translation means, said voltage divider changing the relative density -of at least two `of the electron streams generated by the electron lguns coupled thereto, said voltage divider being manually adjustable for changing the color of the light output from said target along Plancks temperature locus.

5. In a color television receiver including a picture tube having three electron guns -displaced from .aV mosaic target consisting of a plurality of groups of red, green and blue light emitting phosphors, each phosphor in each -of said groups emitting its associated colored light upon bombardment `by an electron stream from a corresponding one of said three electr-on guns, scansion means deflecting said beans horizontally and vertically to produce a raster on said tube;

each said electron gun having an electrode system capable of controlling the density of said electron stream genera-ted thereby;

bias means coupled to said electrode systems controlling the no signal bombardment level for said different colored-light emitting phosphors and establishing a point on the color temperature illumination line;

three color dilerence amplifiers having outputs coupled to the electrode systems of each of said electron guns respectively;

demodulator means supplying red, green and blue color difference signals to the inputs of said color dilerence amplifiers, respectively;

a voltage divider coupled to the outputs of ythe green and blue color difference .amplifiers for changing the relative density of the electron streams generated by the electron guns coupled thereto, said voltage divider being manually adjustable along a divider ratio for shifting the color 4of said raster substantially along Plancks temperature locus.

References Cited 

1. IN A COLOR TELEVISION RECEIVER INCLUDING A PICTURE TUBE HAVING AN ELECTRON GUN BEAM GENERATION SYSTEM DISPLACED FROM A TARGET CONSISTING OF A PLURALITY OF GROUPS OF DIFFERENT COLORED-LIGHT EMITTING PHOSPHORS, AND MEANS PROVIDING SCANSION OF SAID TARGET BY AN ELECTRON BEAM TO PRODUCE A RASTER; EACH PHOSPHOR IN EACH OF SAID GROUPS EMITTING ITS ASSOCIATED COLORED-LIGHT UPON BOMBARDMENT BY ELECTRONS FROM SAID ELECTRON GUN SYSTEM; SAID ELECTRON GUN SYSTEM INCLUDING ELECTRODE MEANS CAPABLE OF CONTROLLING THE ELECTRON BEAM DENSITY THEREOF AND DETERMINING THE BOMBARDMENT LEVEL FOR SAID DIFFERENT PHOSPHORS TO ESTABLISH A GIVEN COLOR TO SAID RASTER; AND MEANS COUPLING A VOLTAGE TO SAID ELECTRODE MEANS FOR SIMULTANEOUSLY CHANGING THE RELATIVE BOMBARDMENT LEVELS OF AT LEAST TWO OF SAID DIFFERENT COLORED-LIGHT EMITTING PHOSPHORS, REGULATION MEANS DETERMINING THE RATIO OF THE SIMULTANEOUS CHANGE IN THE RELATIVE BOMBARDMENT LEVELS AS BETWEEN SAID TWO DIFFERENT COLORED PHOSPHORS, AND SAID REGULATION MEANS CAUSING THE COLOR OF SAID RASTER TO VARY SUBSTANTIALLY ALONG LANCK''S TEMPERATURE LOCUS. 